Buyers or sellers?
The Nationals are in last place in the National League East with a 30-68 record, the worst in the major leagues. They will be looking to sell off expensive veterans in hopes of getting good, young talent that will help the tea when they can eventually contend.
Short-term need
Pitching, pitching, pitching. The club won't be competing in the near future so they've got some time to find some pitching but until then they won't get much better. The rotation is a collection of marginal guys who can't miss bats and the bullpen is just an absolute mess. The Nats aren't big spenders in free agency so they should search around and try to find some useful arms out of the bargain-bin to make the team watchable.
The Nats have lots of corner bats there is a complete lack of middle-infield talent throughout the organization. Finding some talented middle-infielders should be the secondary priority after rebuilding the pitching staff.
Long-term need
More pitching. Seriously, it's hard to overstate the need to upgrade the pitching staff up and down the organization. Jordan Zimmerman and (potentially) Stephen Strasburg are a nice duo to begin the task but the Nats will need to empasize adding arms in the draft and looking for any hidden gems they can find. There isn't a lot of help from the farm system on the horizon so they will just have to be patient. This is a process that will take a few years at least. It would be a nice start if the front office can flip some of the older players for prospects to help get them started. This situation could look quite a bit better if the Nats can add a few arms with upside at the deadline.
On offense the club again needs to add more middle-infield talent. There should be plenty of outfielders for the next few years between Nyjer Morgan, Elijah Dukes (provided he can overcome his struggles this year), and whoever is left over from the trade candidates. Ryan ZImmerman is a franchise cornerstone at third base and catcher and first base should be adequately filled by players in the organization.
Big leaguers on the market?
While no one is sure who will stay and who will go, potentially anyone on the team save for a few young players could find themselves wearing a different uniform in August. Ryan Zimmerman isn't on the block but nearly every other position player is depending on the price, most notably Adam Dunn and Nick Johnson. As for the pitching staff Jordan Zimmerman is probably someone to build around but there's not much else to get excited about. Other potential trade candidates include Josh Willingham, Willie Harris, and Joe Beimel.
Minor league strength
The Nats farm system isn't particularly good, there's not much upper-level talent or many high-upside players. First baseman Chris Marrero has a well-rounded offensive approach but doesn't have prototypical power for his position and is in his third year a the High-A level. Outfielder Michael Burgess was perhaps the Nats top hitting prospect heading into '09 but his numbers at High-A have been wholly unexciting. Left-handed pitcher Ross Detwiler doesn't have the velocity that made him a top-10 pick in the draft two years ago anymore. He is currently in the majors but is 0-5 with a 6.40 ERA.
On a brighter note, 20 year-old catcher Derek Norris looks very promising. He's currently in Single-A .310/.410/.572 with 24 doubles, 21 homeruns, and 54 walks in 395 PA. Also known for his strong throwing arm, Norris is a player to keep an eye on.
Perhaps the two biggest "strengths" of the system though are the Natonals #1 pick in 2009 and their likely #1 pick in 2010. The former was used to select uber-prospect Stephen Strasburg. If the Nats can sign him they instantly add a potential ace on a fast track to the big leagues. The #1 pick next year should let the Nats add another elite talent, perhaps 16 year-old phenom Bryce Harper.
Take on short-term money to win?
There's obviously no reason for the Nats to add any contracts in trades. They will most likely shed some salary as they trade off their older players.
For more coverage of the Nationals, check out Federal Baseball.